1. Field of the Invention
The present invention relates to an imaging apparatus, a radiation imaging apparatus, and a radiation imaging system. For the purpose of this description, the term “radiation” also encompasses electromagnetic waves such as X-rays and γ-rays, α-rays, and β-rays.
2. Description of the Related Art
Recently, known flat-panel photoelectric conversion apparatuses and radiation imaging apparatuses include an area sensor array in which an amorphous silicon or polysilicon film formed on an insulating substrate, such as a glass substrate, is used as a material and pixels composed of photoelectric conversion elements and thin-film transistors (TFTs) are two-dimensionally arrayed. In these apparatuses, by driving the TFTs in a matrix manner, charges that have been subjected to photoelectric conversion in the photoelectric conversion elements are transferred to a reading-circuit unit and read out.
An apparatus according to the related art will now be described. A known flat-panel area sensor includes a sensor array in which pixels composed of amorphous silicon PIN photodiodes and TFTs, which are formed on a glass substrate, are two-dimensionally arrayed. The area sensor is driven in a matrix manner. A bias voltage is applied from a power supply to the common electrode side of the PIN photodiode of each pixel. A gate electrode of the TFT of each pixel is connected to a common gate line, and the common gate line is connected to a gate-driving circuit unit composed of a shift register.
On the other hand, a source electrode of each TFT is connected to a common signal line, which is connected to a reading-circuit unit including an operational amplifier, a sample and hold circuit, an analogue multiplexer, a buffer amplifier, and so forth.
Analog signals output from the reading-circuit unit are digitized by an A/D converter and processed by an image-processing unit composed of a memory, a processor, and the like. The processed signals are then output to a display apparatus such as a monitor or stored in a recording apparatus such as a hard disk.
European Patent Publication No. 0796000, U.S. Pat. No. 5,184,018, and Japanese Patent Laid-Open No. 2004-031658 describe in detail a flat-panel photoelectric conversion apparatus and radiographic apparatus that acquire image signals by driving an area sensor array in a matrix manner using a reading-circuit unit and a gate-driving circuit unit as described above.
All the patent documents describe not only a basic operation of the area sensor but also a configuration in which the reading-circuit unit includes a first-stage amplifier connected to each common signal line, and/or a multiplexer. In some of the documents, the reading-circuit unit further includes multistage amplifiers. Furthermore, the documents also disclose an example of an amplifier made of a crystal semiconductor.